RL setting will be ignored when display
with RAM (Dmode[1:0] = 00).
Yes, I had seen that. However, SSD1289, SSD1297 have the same caveat. And RL works fine on those controllers.
No, I have not tried src.ino yet.
I have only tried GxTFT_graphicstest.ino with my_1.6_transflective_SSD1283A_Uno.h and my_2.8_blue_ili9341_UNO.h
All the other examples are too big for a Uno. They don't build on M0 or STM32.
I can dig out an ESP32. Plenty of SRAM, speed etc. No way to use JTAG or SWD.
I could dig out Teensy3.2. No way to use SWD.
There is nothing unusual with a datasheet that has "feature(s)"
It is often worth trying an undocumented bit. Or just to check whether the chip does actually do what the datasheet says.
David.